The present invention relates to amplifiers and, more particularly, to monolithic integrated differential and operational amplifiers.
Monolithic differential and/or operational amplifiers are utilized in myriad of applications as is well understood. In the past, it has been a goal to produce amplifiers with low quiescent power consumption but such prior art amplifiers have been defficient in in output drive current and alternating current (AC) performance. In fact, it is still the goal to provide an operational amplifier that has high drive current capability in order to drive low impedance loads while also having minimum bias drain current to reduce power consumption. In portable battery powered applications such as mobile telephones, consumer entertainment systems e.g., radios and video games etc., it is especially important to limit the quiescent power consumption of amplifiers used in such applications.
Most, if not all, high output current operational amplifiers are comprised of an input stage that is coupled to an output stage. In response to an alternating input signal being applied to the input stage, the operational amplifier both sources and sinks drive current to and from a load coupled to the output stage. Typically, the input and output stages are biased to a quiescent drain current to permit quality audio and data processing applications. For example, low power, high output current amplifiers such as the MC 33178 manufactured by Motorola, Inc. draw approximately 420 microamperes of drain current per amplifier in the quiescent operating mode with no input signal applied thereto. For micro-power and battery powered applications there is a need to reduce drain current requirements over the foregoing while providing amplifiers that can supply high load currents.
Hence, a need exists for differential and/or operational amplifiers that have reduced drain current requirements over the prior art, absence an applied input signal, but which are responsive to an input signal to provide high load current.